The exchange of ideas is essential to everyone, regardless of their vocation or position. This exchange is usually carried on by oral or written word; but under some conditions, the use of these alone is impractical. The aviation industry discovered that it could not depend entirely upon written or spoken words for the exchange of ideas, because misunderstanding and misinterpretation arose frequently. A written description of an object can be changed in meaning just by misplacing a comma, and the meaning of an oral description can be completely changed by using a wrong word. To avoid these possible errors, drawings are used to describe objects. For this reason, drawing is the draftsman’s language.

Drawing, in the aviation industry, is a method of conveying ideas concerning the construction or assembly of objects. This is done with the help of lines, notes, abbreviations, and symbols. It is important that the aviation mechanic who is to make or assemble the object understands the meaning of the different lines, notes, abbreviations, and symbols that are used in a drawing. (See the “Lines and Their Meanings” section of this chapter.)

From the early days of aviation, development of aircraft, aircraft engines, and other components relied heavily on aircraft drawings. For most of the 20th century, drawings were created on a drawing “board” with pen or pencil and paper. With the introduction and advancement of computers in the later decades of the 20th century, the way drawings are created changed dramatically. Computers were used not only to create drawings, but they were being used to show items in “virtual reality,” from any possible viewing angle. Further development of computer software programs allowed for assembling of separately created parts to check for proper fit and possible interferences. Additionally, with nearly instantaneous information sharing capability through computer networking and the Internet, it became much easier for designers to share their work with other designers and manufacturers virtually anytime, anywhere in the world. Using new computer-controlled manufacturing techniques, it became possible to design a part and have it precisely manufactured without ever having shown it on paper. New terms and acronyms became commonplace. The more common of these terms are:

As computer hardware and software continue to evolve, a greater amount of CAE is completed in less time, at lower cost. In addition to product design, some of the other uses of CAE are product analysis, assembly, simulations, and maintenance information. [Figure 4-1]

CATIA, ProEngineer, Solid Works, and Unigraphics are some of the more popular CAD software packages used for aircraft design and manufacturing. Most airframe manufacturers use CATIA software to design their aircraft. The complete aircraft is designed and assembled in the software package before it is manufactured. Drawings of all parts of the aircraft are available and can be accessed using the computer software. Drawings are no longer limited to 1, 2, or 3 views. Drawings from every angle can easily be accessed by using the computer model of the part or product. Technicians can access drawings and aircraft manuals on laptops or even mobile devices when performing maintenance on the shop floor.

Drawings and prints are the link between the engineers who design an aircraft and the workers who build, maintain, and repair it. A print may be a copy of a working drawing for an aircraft part or group of parts, or for a design of a system or group of systems. They are made by placing a tracing of the drawing over a sheet of chemically-treated paper and exposing it to a strong light for a short period of time. When the exposed paper is developed, it turns blue where the light has penetrated the transparent tracing. The inked lines of the tracing, having blocked out the light, show as white lines on a blue background. With other types of sensitized paper, prints may have a white background with colored lines or a colored background with white lines.

Drawings created using computers may be viewed on the computer monitor or printed out in “hard copy” by use of an ink jet or laser printer. Larger drawings may be printed by use of a plotter or large format printer. Large printers can print drawings up to 42 inches high with widths up to 600 inches by use of continuous roll paper. [Figure 4-2]

Drawings should be handled carefully as they are both expensive and valuable. Open drawings slowly and carefully to prevent tearing of the paper. When the drawing is open, smooth out the fold lines instead of bending them backward.

To protect drawings from damage, never spread them on the floor or lay them on a surface covered with tools or other objects that may make holes in the paper. Hands should be free of oil, grease, or other unclean matter that can soil or smudge the print.

Never make notes or marks on a print, as they may confuse others and lead to incorrect work. Only authorized individuals are permitted to make notes or changes on prints, and they must sign and date any changes they make.

When finished with a drawing, fold and return it to its proper place. Prints are folded originally in an appropriate size for filing. Care should be taken so that the original folds are always used.

Drawings must give information such as size and shape of the object and all its parts, specifications for material to be used, how the material is to be finished, how the parts are to be assembled, and any other information essential to making and assembling the object. Drawings may be divided into three classes: detail, assembly, and installation.